The distribution and dynamic properties of intracellular filamentous structures will be studied in the fish retina and in selected regions of the brain. These structures include 100 A diameter neurofilaments, 250 A diameter microtubules, and 50 A diameter microfilaments. Experiments will be conducted to determine optimal procedures for preservation for electron microscopy and to determine the effects of physical and chemical agents upon the filamentous structures. Physiological experiments on the light-stimulated mechanism of lengthening and shortening in photoreceptor cells and migration of pigment granules will be continued. BIBLIOGRAPHIC REFERENCES: Potter, H.D. 1975 Distribution and Dynamic Properties of Neurofibrils. In: Golgi Centennial Symposium: Perspectives in Neurobiology, M. Santini, editor. Raven Press, New York. pp. 167-175. Potter, H.D., G.S. Hafner, and I.R. Schwartz 1975 Neurofilament and glycogen changes during cold acclimation in the trochlear nucleus of lizards (Sceloporus undulatus). J. Neurocytol. 4: 491-503.